In the prior art, welding cables are fitted and connected to other welding cables or welding equipment through plug and socket. The inner wall of the insertion hole of the socket is provided with a guide slot along the axis direction of the insertion hole. The end of the guide slot is connected to a spiral slot. The spiral slot is arranged at the inner annular surface of the insertion hole, and the axis of the spiral slot coincides with the axis of the insertion hole. The front end of the plug is provided with a protruded locking head. During connection, the plug is inserted along the guide slot of the socket, and then the plug is rotated so as to make the locking head of the plug rotate along the spiral slot. The end face of the plug closely fit the end face of the socket after tightening. In this structure, as both, the plug and the socket are of integral steel structure, the operating distance between tightening and loosening is only 1-2.5 mm during use. During production and operation, the locking head of the plug easily gets loose from the slot due to factors such as handling, vibration, collision, expansion and contraction, and pulling of cables etc. The loosening of the locking head causes insufficient connection and unstable current on the contacting surface. When large current flows through, the plug and socket will heat up, and may burn the connector, thereby causing fire hazards.